Rotor blades, such as those in a helicopter, blades of wind turbines and the like, are subject to erosion caused by the impact of airborne material, such as rain, sand, dust, and other debris. The leading edge of a rotor blade is particularly prone to damage by erosion. Examples of other articles used outdoors subject to erosion include train underfloors and certain portions of the fuselage or a wing of an aircraft.
The industry has sought ways of protecting against such erosion by means of, for example, protective tapes or films. However, the application of tapes or films on, for instance, rotor blades, cannot be easily automated and is typically done by hand. That process can be time-consuming, especially when applying films to blades of large dimensions, as may be the case for those in wind turbines, whose blades may have a length greater than 30 m, or even greater than 60 m. The next generation of wind rotor blades are expected to have lengths of more than 100 m.
The present inventors propose that two-part polyurethane coatings comprising an isocyanate composition (part A) and a hydroxyl composition (part B) may be used as erosion-protection materials. Normally, two-part polyurethane coatings are very sensitive to high relative humidity during curing because the isocyanate composition reacts with water, which results in a loss of performance. This lower performance often leads to limitations in the areas in which those polyurethane coatings can be used.
For that reason, two-part polyurethane coatings are often only used in environments where humidity and temperature are controlled or where a drop in performance is accounted for and calculated into the application. In certain industries, such as the wind industry, it is not possible to control the humidity and temperature during the application of the polyurethane coating, and a drop in performance cannot be allowed. In those circumstances, manufacturers may need to wait until the environmental humidity is within an acceptable range before coating blades with two-part polyurethane materials.
In operations & maintenance situations, where turbine blades have to be repaired in the field, the repairs may need to wait until weather conditions are suitable or the repair may need to be done outside of the application window, which would result in poor material performance.
Thus, there is a need in the art for two-part polyurethane coatings that can be applied under high humidity conditions, without displaying unacceptable performance losses. Such two-part polyurethane coatings are disclosed in some embodiments of the present application.